The present invention relates to an improved method of forming blown plastic articles wherein biaxial orientation of the thermoplastic material occurs during the formation of the blown article.
Advantages of biaxial orientation of thermoplastic material are well known and are set forth in the prior art, for example, in U.S. Pat. Nos. 3,470,282 and 3,767,747 and the references cited therein. Efforts have recently been made to utilize the phenomenon of biaxial orientation of thermoplastic material in conjunction with conventional blow molding machines. One such effort is disclosed in aforesaid U.S. Pat. No. 3,767,747 in which a blow molding method is proposed that is particularly adapted for utilization for the so called "free extrusion" blow molding machines wherein a pendent tube of thermoplastic material is issued from a downwardly facing orifice.